Turning to FIG. 1 there is shown a pulse power circuit known in the art. The pulse power circuit may include, e.g., a high voltage resonant power supply 30, commutator module 40, compression head module 60 and a laser chamber module 80. High voltage power supply module 20 can comprise, e.g., a 300 volt rectifier 22 for, e.g., converting the 208 volt three phase normal plant power from source 23, 10 to 300 volt DC. An inverter 24, e.g., converts the output of rectifier 22 to, e.g., high frequency 300 volt pulses in the range 100 kHz to 200 kHz. The frequency and the on period of inverter 24 can be controlled, e.g., by a HV power supply control board (not shown) in order to provide course regulation of the ultimate output pulse energy of the system, e.g., based upon the output of a voltage monitor 44 comprising, e.g., a voltage divider having, e.g., resistors VDR1, and VDR2.
The output of inverter 24 can be stepped up to about 1200 volts in step-up transformer 26. The output of transformer 26 is converted to 1200 volts DC by rectifier 28, which can include, e.g., a standard bridge rectifier circuit 28 and a filter capacitor 32. The DC output of circuit 20 can be used, e.g., to charge, e.g., an 8.1 μF charging capacitor C0 42 in commutator module 40 as directed by HV power supply control board (not shown), which can, e.g., control the operation of inverter 24. Set points, e.g., within HV power supply control board (not shown) can be provided by a laser system control board (not shown). In the discussed embodiment, e.g., pulse energy control for the laser system can be provided by power supply module 20.
The electrical circuits in commutator module 40 and compression head module 60 may, e.g., the serve to amplify the voltage and compress the electrical energy stored on charging capacitor C0 42 by power supply module 20, e.g., to provide 700 volts to charging capacitor C0 42, which during the charging cycle can be isolated from the down stream circuits, e.g., by solid state switch 46.
In the commutator module 40, which can comprise, e.g., charging capacitor Co 42, which can be, e.g., a bank of capacitors (not shown) connected in parallel to provide a total capacitance of, e.g., 8.1 μF, along with the voltage divider 44, in order to, e.g., provide a feedback voltage signal to the HV power supply control board (not shown) which is used by control board (not shown) to limit the charging of charging capacitor C0 42 to a voltage (so-called “control voltage”), which, e.g., when formed into an electrical pulse and compressed and amplified in the commutator 40 and compression head 60, can, e.g., produce the desired discharge voltage on a peaking capacitor Cp 82 and across electrodes 83 and 84.
As is known in the art, the prior art circuit of FIG. 1 may be utilized to provide pulses in the range of 3 or more Joules and greater than 14,000 volts at pulse rates of 2,000–4,000 or more pulses per second. In such a circuit, e.g., about 250 microseconds may be required for DC power supply module 20 to charge the charging capacitor C0 42 to, e.g., 700 volts. Charging capacitor C0 42, therefore, can, e.g., be fully charged and stable at the desired voltage, e.g., when a signal from a commutator control board (not shown) is provided, e.g., to close a solid state switch 46, which, e.g., initiates a very fast step of converting the 3 Joules of electrical energy stored on charging capacitor C0 42 into, e.g. a 14,000 volt or more charge on peaking capacitor Cp for creating a discharge across electrodes 83 and 84. The solid state switch 46 may be, e.g., an IGBT switch, or other suitable fast operating high power solid state switch, e.g., an SCR, GTO, MCT, high power MOSFET, etc. A 600 nH charging inductor L0 48 is in series with solid state switch 46 may also be employed, e.g., to temporarily limit the current through the solid state switch 46 while it closes to discharge the charge stored on charging capacitor Co 42 onto a first stage capacitor C1 52, e.g., forming a first state of pulse compression 50.
For the first stage 50 of pulse generation and compression, the charge on charging capacitor C0 42 is thus switched onto a capacitor, e.g., a 8.5 μF capacitor C1 52, e.g., in about 5 μs. A saturable inductor 54 holds off the voltage on capacitor C1 52 until it saturates, and then presents essentially zero impedance to the current flow from capacitor C1 52, e.g., allowing the transfer of charge from capacitor C1 52 through a, e.g., 1:23 step up pulse transformer 56 to charge capacitor Cp-1 capacitor 62 in the compression head module 60, with, e.g., a transfer time period of about 550 ns, comprising a first stage of compression.
The design of pulse transformer 56 is described in a number of prior patents assigned to the common assignee of this application, including, e.g., U.S. Pat. No. 5,936,988 referenced above. Such a transformer is an extremely efficient pulse transformer, transforming, e.g., a 700 volt 17,500 ampere, 550 ns pulse, e.g., a 16,100 volt, 760 ampere 550 ns pulse, which, e.g., is stored very temporarily on compression head module capacitor Cp-1 62, which may also be, e.g., a bank of capacitors. The compression head module 60 may, e.g., further compress the pulse. A saturable reactor inductor Lp-1 64, which may be, e.g., about a 125 nH saturated inductance, can, e.g., hold off the voltage on capacitor Cp-1 62 for approximately 550 ns, in order to, e.g, allows the charge on Cp-1 to flow, e.g., in about 100 ns, onto a peaking capacitor Cp 82, which may be, e.g., a 16.5 nF capacitor located, e.g., on the top of a laser chamber (not shown) and which the peaking capacitor Cp 82 is electrically connected in parallel with electrodes 83 and 84. This transformation of a, e.g., 550 ns long pulse into a, e.g., 100 ns long pulse to charge peaking capacitor Cp 82 can make up, e.g., the second and last stage of compression. About 100 ns after the charge begins flowing onto peaking capacitor Cp 82 mounted on top of and as a part of the laser chamber (not shown) in the laser chamber module 80, the voltage on peaking capacitor Cp 82 will have reached, e.g., about 14,000 volts and a discharge between the electrodes 83 and 84 begins. The discharge may last, e.g., about 50 ns, during which time, e.g., lasing occurs within the resonance chamber (not shown) of the, e.g., excimer laser.
The circuitry of the prior art FIG. 1 may also include, e.g., a bias circuit defined by bias current source I− and a bias current I+. Bias inductors, e.g., inductors LB1, and LB2 may be connected, e.g., to bias current source I− and I+, respectively, and also to, e.g., first stage compressor circuit 50, e.g., between a diode 47 on the output of solid state switch 46 and charging inductor L0 48 and between compression head capacitor Cp-1 62 and compression head saturable inductor Lp-1 64, respectively. Bias current source I− can, e.g., supply a bias, which can, e.g., presaturate saturable inductor L1. Inductor LB1 may, e.g., have a relatively high inductance value to provide a relatively long time constant in the bias circuit relative to those of compression head module 60, thereby, e.g., isolating bias current source I+ from pulse power. Similarly bias current I+ can bias compression head saturable inductor Lp-1 64 (returning to ground through bias inductor LB3) and pulse transformer 56 (returning to ground through the transformer 56 secondary winding.
After the discharge between the electrodes 83, 84 capacitor Cp may be driven to a negative polarity charge, e.g., because of an impedance mismatch between circuit 40, 50, 60, 80 and the laser chamber module electrodes 83, 84, and, e.g., because saturable inductor Lp-1 is already presaturated with respect to forward current from capacitor Cp-1 to capacitor Cp, instead of having energy ringing between the electrodes 83, 84, for example eroding the electrodes 83, 84, the reverse charge on capacitor Cp is instead transferred resonantly back into capacitor Cp-1 and so forth back to capacitor C0, precharging capacitor C0 before charging from the power supply 20 for the next pulse. In this manner, the electronic circuitry can, e.g., recover excess energy on charging capacitor C0 42 from the previous pulse which substantially reduces waste energy and virtually eliminates after ringing in the laser chamber module 80.
This is facilitated also by, e.g., an energy recovery circuit 57, which may be composed of, e.g., energy recovery inductor 58 and energy recovery diode 59. The series combination of the two connected in parallel across charging capacitor Co 42 can, e.g., because the impedance of the pulse power system is, e.g., not exactly matched to that of the chamber and due, e.g., to the fact that the chamber impedance varies several orders of magnitude during a pulse discharge, a negative going “reflection” may be generated from the main pulse across the electrodes 83, 84, which can propagate back towards the front end of the pulse generating system 40, 50, 60, 80.
After the excess energy has propagated back through the compression head 60 and the commutator 40, solid state switch 46 opens up, e.g., due to the removal of the trigger signal for solid state switch 46 by the controller (not shown). The energy recovery circuit 57 can, e.g., reverse the polarity of the reflection which has generated a negative voltage on the charging capacitor C0 42 through, e.g., resonant free wheeling (a half cycle of ringing of the L-C circuit made up of the charging capacitor C0 42 and the energy recovery inductor 58 as clamped against, e.g., reversal of current in inductor 58 due to diode 59). The net result can be that substantially all of the reflected energy from the chamber module 80 can be recovered from each pulse and stored on charging capacitor C0 42 as a positive charge ready to be utilized for the next pulse.
The DC bias circuitry noted above can serve to assist in more completely utilizing the full B-H curve swing of the magnetic materials used in the saturable inductors and the pulse transformer. Also as noted above, a bias current is provided to each saturable inductor L0 48, L1 54 and Lp-1 64 such that each inductor L0 48, L1 54 and Lp-1 64 is reverse saturated at the time a pulse is initiated by the closing of solid state switch 46. In the case of the commutator module 40 saturable inductors L0 48 and L1 54, this is accomplished by providing a bias current flow of approximately 15A backwards, compared to the normal pulse current flow, i.e., in the direction of I− from bias current source 120 through the inductors L0 48 and L1 54. Actual current flow travels from the power supply through the ground connection of the commutator, through the primary winding of the pulse transformer 56, through saturable inductor L1 54, through saturable inductor L0 48, and through isolation inductor LB1 back to the bias current source 120 as indicated by arrows B1. In the case of compression head saturable inductor, e.g., a bias current B2 of approximately 5A is provided from a second bias current source 126 through isolation inductor LB2. At the compression head module 60, the current splits and a fraction goes through saturable inductor Lp-1 64 and back through isolation inductor LB3 back to the second bias current source 126. The remainder of the current B2-2 travels back through an HV cable connecting the compression head module 60 and the commutator module 40, through the pulse transformer 56 secondary winding to ground, and through a biasing resistor (not shown) back to the second bias current source 126. This second current may be used, e.g., to bias the pulse transformer 56, e.g., so that it is also reset for the pulsed operation. The amount of current which splits into each of the two legs may be determined, e.g., by the resistance in each path and may be adjusted such that each path receives the correct amount of bias current.
The flow of pulse energy through the system 40, 50, 60, 80 from the plant power source 23 to the electrodes 83, 84 and to ground beyond electrode 84 as referred to as “forward flow” and this direction as the forward direction. When referring to an electrical component such as a saturable inductor as being forward conducting, this mean that it is biased into saturation to conduct “pulse energy” in a direction toward the electrodes—the forward direction. When it is reverse conducting it is driven into saturation in the reverse direction, and may be biased in such direction. The actual direction of current flow (or electron flow) through the system depends on the point of observation within the system and the time of observation.
Charging capacitor C0 42 may be charged with (for example) a positive 700 volts such that when solid state switch 46 is closed current flows from charging capacitor C0 42 through charging inductor L0 48 and first stage compression inductor L1 in a direction toward first stage compression capacitor C1 52. Similarly, the current flow is from C1 52 through the primary side of pulse transformer 56 toward ground. Thus, the direction of current and pulse energy is the same from charging capacitor C0 42 to pulse transformer 56. Current flow in both the primary loops and the secondary loop of pulse transformer 56 may both be, e.g., toward ground.
Solid state switch 46 may be an P/N CM 1000 HA-28H IGBT switch provided by Powerex, Inc. of Youngwood, Pa.
It is clear that circuits operating with such high voltages and currents and more particularly including magnet circuit components operating at very high pulse repetition rates, e.g., up to 4000 Hz or more, generate extreme amounts of heat. This is perhaps most critical for the compression head magnetic saturable inductor/reactor Lp-1, but is applicable to all of the saturable reactors/inductors in the pulse power supply system 40, 50, 60, 80. It is also a critical factor of operation of the step up pulse transformer 56. In the past these magnetic circuit elements have been cooled using, e.g., a cold plate with one or more passages through the plate, usually separated by substantial expanses of cold plate between such passages, e.g., as shown in U.S. Pat. No. 5,448,580, issued to Birx, et al. on Sep. 5, 1995, entitled AIR AND WATER COOLED MODULATOR, on a application Ser. No. 270,718, filed on Jul. 5, 1994. Cooling has also been proposed by conductively coupling, e.g., a coil of piping containing cooling liquid, e.g., water, in contact with the outside of the housing of such a magnetic circuit element, e.g., as shown in U.S. Pat. No. 6,442,181, entitled EXTREME REPETITION RATE GAS DISCHARGE LASER, issued to Oliver, et al. on Aug. 27, 2002, on an application Ser. No. 09/684,629, filed on Oct. 6, 2000, as a continuation-in-part of Ser. No. 09/370,739, filed Aug. 9, 1999 now U.S. Pat. No. 6,151,346, which was a continuation-in-part of Ser. No. 09/118,773, filed Jul. 18, 1998 now U.S. Pat. No. 5,936,988 and Ser. No. 09/608,543, filed Jun. 30, 2000, all of which are assigned to the common assignee of the present application, and the disclosures of which are hereby incorporated by reference. This patent also shows an even less effective method of using heat sink type cooling fins on the outside of the housing of such a magnetic circuit element. Of course liquid had also been put into the housing in contact with the conductors and core magnetic pieces, which, for obvious reason must be a dielectric, e.g., transformer oil or other suitable dielectric cooling fluid, e.g., Brayco Micronic 889 made by Castrol, or any of a number of well known Fluorinert compounds. Such liquid insulators may prove to be unacceptable, in part, due to a tendency to break down with sloid particulate or water or other contaminant over time. U.S. Pat. No. 4,983,859, entitled MAGNETIC DEVICE FOR HIGH-VOLTAGE PULSE GENERATING APPARATUSES, issued to Nakajima, et al. on Jan. 8, 1991 also proposes using such a fluid and circulating it through the inside of the housing. Such a system, among other drawbacks, could not be used in a facility having high clean room requirements, i.e., semiconductor manufacturing facilities, because of the need to pump and circulate the cooling oil. Other prior art uses include using such a fluid statically sealed within the housing, which may, e.g., due to convection currents in the fluid cause circulatory action within the housing which may serve to at least assist in carrying heat energy away from the conductors and magnetic pieces generating the principal amounts of the heat energy to the housing for further heat exchange as discussed in the art referenced above.
With the even higher requirements for voltage and pulse repetition rate and reduced time between pulse bursts, i.e., a higher duty cycle, the heat energy released in such magnetic circuit elements is increasingly more difficult to mediate. This is even more critical in machines such as laser light sources for, e.g., UV and EUV and shorter wavelength light requiring very high pulses of very high pulse repetition rate with very narrow, on the order of 1 ns or less pulse duration with very little lack of variation pulse to pulse, due to critical magnetic characteristics of magnetic circuit elements used in such pulse generation equipment being very susceptible to temperature related drift, at least, if not failure to properly perform unless temperatures are more tightly controlled than has ever before been the case. The prior art methods and apparatus discussed above and their equivalents have served for past requirements but are rapidly becoming, if not already, inadequate. There is a need, therefore in the art of such magnetic circuit elements for an improved method and apparatus for the removal of the heat energies generated by the conductors, magnetic core pieces and the like while maintaining electrical isolation between parts being cooled and without the use of circulated fluids, e.g., such as oil, which can potentially be detrimental to, e.g., clean room environments.
The physical structure of the pulse step up transformer is also described in a number of prior patents assigned to the common assignee of the present application, including, e.g., U.S. Pat. No. 6,151,346, issued to Partlo, et al. on Nov. 21, 2000, entitled HIGH PULSE RATE PULSE POWER SYSTEM WITH FAST RISE TIME AND LOW CURRENT and U.S. Pat. No. 5,940,421, issued to Partlo, et al. on Aug. 17, 1999, entitled, CURRENT REVERSAL PREVENTION CIRCUIT FOR A PULSED GAS DISCHARGE LASER, referenced above.
In high voltage applications, such as those just discussed, it is necessary to have an electrical insulator between two conducting metal parts in order to hold off the applied voltage with a potential difference between individual parts. In many cases air alone, though an insulator, is not sufficient. Furthermore, in many cases insulation between such metallic parts may need to exist in more than one axis. In known inductors utilized in known circuits, such as those just discussed, an insulator, such as Kapton (polyimide), may have been used to isolate metallic components. In such case, e.g., in the inductor housing shown in FIG. 8B of the above referenced U.S. Pat. No. 5,936,988, a sheet of insulator, e.g., Kapton, may be utilized by inserting it between the inner wall of the housing shown in that Figure and the metallic elements, e.g., magnetic cores 301 and 302 shown in that Figure, i.e., forming a cylinder generally abutting the interior wall of the inductor housing. Also in known inductors this sheet may form a cylinder abutting another interior cylindrical wall formed within the interior of the housing (not shown in that Figure). A sheet of such material may also be cut to an appropriate shape and size and inserted into the housing to cover, e.g., the housing floor and separate the housing floor from nearby electrically energized metallic components within the housing. Such arrangements have proved unsatisfactory for a number of reasons, including the propensity for improper fit and/or the existence of deformations causing, e.g., gaps in the coverage allowing arcing and other undesirable effects (e.g. air bubbles may also form between the insulator sheet and the housing, leading to dielectric mis-match conditions and electric field enhancements which may then cause electrical breakdowns).
Alternatively, where form and fit allow, which will not always be the case, it might be possible to machine, e.g., an open ended toroidally shaped piece of the insulating material and to place a similarly shaped toroidal component within the opening. This however, could be very expensive, as the machined out insulating material, e.g., Mylar or Kapton, would simply have to be discarded. In addition, gaps and the attendant problems could still arise where another sheet of the insulating material is used to attempt to close the opening at the top of the open toroidal insulation structure.
It is desirable, therefore to find a solution to these problems in high power high pulse rate magnetic circuit elements and the like.